1. Field of the Invention
The present invention relates to a package structure. More particularly, the present invention relates to a chip on photosensitive device package structure and electrical connection thereof.
2. Description of Related Art
Charge coupled device (CCD) is one of the most common image sensors. The advantages of CCD include high dynamic range, low dark current and relatively mature development. However, CCD is rather expensive to produce due to many special fabrication processes and also the use a high driving voltage by the CCD incurs higher power comsumption. Furthermore, CCD do not allow random accessing of the image points.
In contrast, complementary metal-oxide-semiconductor (CMOS) image sensors has high quantum efficiency, low read-out noise, high dynamic range and random accessing capacity. Furthermore, the fabrication of CMOS image sensors is compatible with other CMOS processes. Hence, it is fairly easy to fabricate other control circuits, analogue/digital converters and digital signal processing circuits on the same chip and produce a self-contained unit, the so-called system on a chip (SOC). In other words, the production cost of the CMOS image sensor as well as the power consumption and the pixel size of CMOS image sensors are reduced considerably. In recent years, CMOS image sensors has found many low-cost applications including the gradual replacement of high cost CCD.
Both the CCD image sensor or CMOS image sensor have an array of photodiodes located within an illumination area. The photodiode array is capable of receiving external image signals (or light intensity signals), converting the image signals into electrical signals and transmitting the electrical signal to a circuit substrate for further image processing. FIG. 1 is a schematic cross-sectional view of a conventional electrical package. As shown in FIG. 1, the electrical package 100 mainly comprises a circuit substrate 110, a photosensitive device 120, an image processing chip 130, and a non-volatile memory 140. The photosensitive device 120 is, for example, a CCD image sensor or a CMOS image sensor set on the upper surface of and electrically connected to the circuit substrate 110. To prevent impurities and micro-particles from contaminating the illumination area 122 of the photosensitive device 120, a transparent plate 124 or transparent layer fabricated from glass is formed on the upper surface of the photosensitive device 120. In general, an external image or light has to penetrate through the transparent plates 124 in order to reach the illumination area 122 of the photosensitive device 120. Thereafter, the image signals are converted into electrical signals by the array of photodiodes (not shown) and the electrical signals are sent to the image-processing chip 130 via the circuit substrate 110 to extract information regarding the flux and degree of color saturation in each pixel of the photodiode array.
It should be noted that the image-processing chip 130 and the non-volatile memory 140 are set on the upper surface or the lower surface of the circuit substrate 110 and then electrically connected to the circuit substrate 110 in the conventional fabrication technique. However, with the image-processing chip 130 and the non-volatile memory 140 occupying some surface area of the circuit substrate 110, further increase in the level of integration of the electrical package through a miniaturization of the substrate 110 is impossible.